(1) Field Of The Invention
This invention relates to the use of foams for shock isolation of equipment and, in particular, to a foam having fibers to prevent the viscoelastic or viscoplastic behavior of the foam.
(2) Description of the Prior Art
Foams are commonly used for shock isolation when transporting equipment, such as on a submarine or surface ship. The environment on a ship or other such vehicle can be damaging to certain systems and/or components which must be transported. In the past, foam padding has been used to provide resistance to the shock and vibration thereby preventing damage to the equipment. However, the weight of a component or piece of equipment supported by the foam padding can cause excessive compression of the foam and reduce the resiliency of the foam, thus reducing its effectiveness as a shock and vibration isolator.
In the prior art, different types of foams were used based on the weight of the equipment to allow the foam to support heavier loads without damaging the foam. One problem with using different types of foams is that a foam which is capable of supporting a greater weight without excessive compression does not deform as easily and offers less shock protection.
Another prior art shock isolation device is disclosed in U.S. Pat. No. 3,283,988 to Hardigg and includes a foam cushioning having a stiff, flexible tube embedded therein. In this shock isolation device, however, the stiff, flexible tubes are flush with the top surface of the foam so that the weight of an object supported by the device will still be resting on the foam. Also, the manufacturing of the prior art shock isolation device is disadvantageous in that the flexible tubes must be embedded in the cushioning material.
Hardigg has several deficiencies when it is used in an application incorporating heavy objects subjected to cyclical loading. One problem is the size of column members needed in Hardigg to support heavy objects. Another problem with the column members of Hardigg is the tendency of an elastomer to heat and melt when subjected to numerous cyclical loadings. Forming the column members within the foam as taught by Hardigg creates problems because the column members tend to separate from the foam on buckling thereby damaging the foam. If the area of foam around the column members is damaged then in a critical loading situation, the foam cannot act to adequately support the columns. Furthermore, if the column members are damaged then the entire element must be replaced. Cyclic loading of the foam in Hardigg can damage the cell structure of the elastomeric padding thereby reducing its cushioning when critical accelerations occur.